Field of the Invention
The present invention relates to a capacitive touch input apparatus of a human finger or a touch input means having conductive characteristics similar thereto, and more particularly, to a touch signal detection apparatus and a touch signal detection method capable of being widely used for a touch detection sensor having different array arrangements.
Discussion of the Background
Generally, a touch screen panel is attached on display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), and an organic light emitting diode (OLED), an active matrix organic light emitting diode (AMOLED) and is one of the input apparatuses that generate signals corresponding to positions where objects such as a finger and a pen are touched. The touch screen panel has been used in wide applications such as small portable terminals, industrial terminals, and digital information devices (DIDs).
Typically, various types of touch screen panels have been disclosed. However, a resistive touch screen panel having simple manufacturing process and low manufacturing costs has been most widely used. However, the resistive touch screen panel has the low transmissivity and needs to be applied with a pressure, For this reason, the resistive touch screen panel is inconvenient to use, has a difficulty in implementing a multi touch and a gesture cognition, leads to a detection error, etc.
On the other hand, a capacitive touch screen panel may have high transmissivity, cognize a soft touch, and implement better multi touch and gesture cognition. As a result, the capacitive touch screen panel is gradually expanding into new markets.
FIG. 1 illustrates an example of the existing capacitive touch screen panel. Referring to FIG. 1, transparent conductive layers are formed on upper and lower surfaces of a transparent substrate 2 made of plastic, glass, etc., and voltage applying metal electrodes 4 are formed at each of the four corners of the transparent substrate 2. The transparent conductive layer is made of transparent metals such as indium tin oxide (ITO) and antimony tin oxide (ATO). Further, the metal electrodes 4 formed at four corners of the transparent conductive layer are formed by being printed with conductive metal having low resistivity such as silver Ag. A resistance network is formed around the metal electrodes 4. The resistance network is formed in a linearization pattern to equally send out a control signal to the whole surface of the transparent conductive layer. Further, an upper portion of the transparent conductive layer including the metal electrode 4 is coated with a passivation layer.
In the capacitive touch screen panel as described above, a high-frequency alternating voltage is applied to the metal electrode 4 and thus is conducted over the whole surface of the transparent substrate 2. In this case, when the transparent conductive layer on an upper surface of the transparent substrate 2 is light touched with a finger 8 or a conductive touch input means, a change in current is sensed by a current sensor embedded in a controller 6 while a predetermined amount of current is absorbed into a body and current amounts at each of the four metal electrodes 4 are calculated, thereby cognizing touched points.
However, the capacitive touch screen panel as illustrated in FIG. 1 is based on a method for detecting a magnitude of micro current. As a result, the capacitive touch screen panel needs an expensive detection apparatus and therefore a price of the capacitive touch screen panel goes up and the capacitive touch screen panel is hard to implement a multi touch for cognizing a plurality of touches.
To overcome the above problems, the capacitive touch screen panel as illustrated in FIG. 2 has been mainly used in recent years. The touch screen panel of FIG. 2 is configured to include a lateral linear touch detection sensor 5a, a longitudinal linear touch detection sensor 5b, and a touch drive IC 7 analyzing a touch signal. The touch screen panel is based on a method for detecting a magnitude of capacitance formed between the linear touch detection sensor 5 and the finger 8 and scans the lateral linear touch detection pad 5a and the longitudinal linear touch detection pad 5b to detect a signal, thereby cognizing the plurality of touched points.
However, when the above-mentioned touch screen panel is installed on a display device such as an LCD, the touch screen panel is hard to detect a signal due to noise. For example, the LCD uses a common electrode applied with a common voltage Vcom that is commonly applied to a liquid crystal. In this case, the common voltage is affected by a pixel voltage applied to the liquid crystal and therefore may be fluctuated. As a result, the common voltage Vcom of the common electrode acts as noise upon detecting the touched point.
Further, unlike the effect of the fluctuation of the common voltage on the touch signal, a scan signal may affect the common voltage upon scanning the lateral linear touch detection sensor 5a and the longitudinal linear touch detection sensor 5b to acquire touch signals to cause deterioration in image quality.
FIG. 3 illustrates an embodiment in which the existing capacitive touch screen panel is installed on the LCD. A display device 200 has a structure in which a liquid crystal is sealed between a TFT substrate 205 at a lower portion thereof and a color filter 215 at an upper portion thereof to form a liquid crystal layer 210. To seal the liquid crystal, the TFT substrate 205 and the color filter 215 are bonded to each other by having a sealant 230 disposed at outer portions thereof. Although not illustrated, polarizing plates are attached to upper and lower portions of a liquid crystal panel and back light units (BLUs) are additionally installed at the liquid crystal panel.
As illustrated, the touch screen panel is installed at the upper portion of the display device 200. The touch screen panel has a structure in which the linear touch detection sensor 5 is put on an upper surface of the substrate 1. A protection panel 3 for protecting the linear touch detection sensor 5 is attached on the substrate 1. The touch screen panel is bonded to an edge portion of the display device 200 by an adhesive member 9 such as a double adhesive tape (DAT), in which an air gap 9a is formed between the touch screen panel and the display device 200.
In this configuration, when a touch is performed as illustrated in FIG. 3, a capacitance such as Ct is formed between the finger 8 and the linear touch detection sensor 5. However, as illustrated, a capacitance such as common electrode capacitance Cvcom is also formed between the linear touch detection sensor 5 and the common electrode 200 formed on a lower surface of the color filter 215 of the display device 200 and an unknown parasitic capacitance Cp that occurs due to a capacitance coupling between patterns, manufacturing process factors, etc., is also applied to the linear touch detection sensor 5. Therefore, a circuit like an equivalent circuit of FIG. 4 is configured.
Here, the existing touch screen panel detects a variation of Ct that is a touch capacitance to cognize a touch and components such as Cvcom and Cp act as noise upon detecting the Ct. In particular, the common electrode capacitance Cvcom may also be ten times larger than the Ct that is the touch capacitance. As a result, there is a problem in that touch sensitivity may be reduced due to a distortion of the touch signals due to the fluctuation of the Cvcom and the touch capacitance ten times larger than the Ct.
To solve the above problem, a touch signal detection method with a new structure to reduce the Cvcom has been proposed. FIG. 5 illustrates an embodiment of a method for reducing Cvcom. The method for reducing Cvcom separates the linear sensor of FIG. 2 into several to reduce the Cvcom, thereby solving problems such as the reduction in sensitivity or the effect on the display device. However, in the structure, since the number of touch detection sensors 10 is more than the number of linear sensors 5 of FIG. 2, the plurality of touch detection sensors 10 need to detect the touch signals to meet a touch signal report time. In this case, upon simultaneously detecting the touch signals in row signals (for example, (Col1, Row1) and (Col1, Row2)) adjacent to the same column, the interference of the touch signals may occur due to the parasitic capacitance Cp between sensor signal lines 22 connected to each of the touch detection sensors 10.
FIG. 6 illustrates an embodiment in which the interference of the touch signals occurs upon simultaneously detecting the touch signals in (C1, R1) 22-a and (C1, R2) 22-b. Referring to FIGS. 5 and 6, a sensing pad signal line 22a of FIG. 6 which is adjacent to the signal line 22b in FIG. 5 is connected to a touch drive IC (TDI) and the parasitic capacitance Cp is formed between the signal line 22a and the signal line 22b. Upon detecting the touch signals by the (C1, R1) touch detection sensor of FIG. 6 using a driving back phenomenon (see Patent Application No. 2012-0109309), the (C1, R1) and the (C1, R2) may be affected to each other due to the parasitic capacitance Cp and therefore an error of the touch signal detection occurs.